Intermittent shimmy

[Rod Frazier 52]

1300 miles into a 4800 mile road trip and the ‘40 Century is exhibiting a minor but annoying intermittent shimmy ((shake, vibration) at all speeds, usually lasting 10 to 30 seconds before smoothing out again.  Any ideas on what to check first?  

[trimacar 3,234]

First thing to check is tire pressures.

[Morgan Wright 970]

The front wheel bearings were tight and packed with grease before the trip, right? The rear wheel bearings on the '40 require a more elaborate grease job. They are not oiled via the axle from the differential, like later models. They need to be packed with grease by removing the half axles, by opening the differential and releasing the C clips. If you greased all 4 wheel bearings and the car is still giving the shimmy and vibration, further investigation is forthcoming.

Edited September 20, 2019 by Morgan Wright (see edit history)

[Bloo 1,663]

And then make sure your steering joints (tierod ends, drag link, etc) are all free of slop, as well as the kingpins. Spin your tires to see that they are still round (no bulges in the tread), and that they do not wobble.

[Terry Wiegand 1,866]

In my humble opinion there are several things that could contribute to a problem.  As David has mentioned, tire pressures are one thing.  Alignment is another issue, along with tire and wheel balance.  All of the joints should be snug and fully greased.  This issue should be able to be eliminated rather easily by going through each area thoroughly.

 

Terry Wiegand

South Hutchinson, Kansas

[Rod Frazier 52]

Tires at 35# at trip beginning.  Complete rear axle bearing and seal kit also.  Did not repack front bearings but I think I had them done about 3000 miles ago.  Perfect alignment has never been possible with this car, which will always pull slightly to the left, but there’s no abnormal tire wear during the last 20000 miles.  I had a major service done before the trip but did not ask for a detailed check of the steering and suspension components since the car was driving so well.  I’m on my way to South Carolina for the VMCCA Glidden tour and plan to get there on the 22nd.  Looks like I need to take some time off the tour to get the car on a rack for a closer look.  One last question:  How would increased tire pressure alleviate a shimmy?  Passing through Tennessee today...wave if you see me!

[trimacar 3,234]

Perfect alignment not possible, you've answered your own question.  Something in the front end is worn, bent, or misaligned .  Good enough isn't good enough for a front end with wear or damage.

 

These cars never had the wobble when sold, or they never would have sold them in the first place.

 

A wobble is a harmonic oscillation, and bouncy under inflated tires just add to the harmonics.....

[auburnseeker 4,513]

Wouldn't 35 lbs be overinflated, causing you to ride on the center of the tire and not the full tread path?

[Terry Wiegand 1,866]

David, please explain to us on here why perfect alignment is not possible on these cars.  On my wife's LeSabre we had to replace one side of the tie rod ends.  The tire shop did an alignment using what I think was a laser based machine and the fellow told me that it was set to be dead on to factory specifications.  I would think that if this can be done on a car such as this, then it could be done on an automobile that has wheels that are not that much different from what is being used today.  Just asking.

 

Terry Wiegand

South Hutchinson, Kansas

[60FlatTop 6,192]

I have had a couple vehicles that would roll over some imperfection in the road and shimmy until I slowed to nearly a stop. Then they were fine until the next little bump. My first check would be the lower outer control arm bushings, then the uppers, next the tie rod ends.

 

Running it up on a lift and shaking things won't show the wear. The suspension needs to be supported to relieve the pressure on those points. That level of service generally only comes at home.

 

I dropped my rusty, 14 year old truck for an oil change last week because my garage was full. I had coffee across the street with the old guys while they did it. I came back and said "Oh, crap, I wanted you to check the bolts that hold the box on. I'm thinking about getting a new one. Can you run it back up and do that?" He told me that would be OK. He never had any trouble with those bolts. I just growled. Then I said "You greased it didn't you?" He said the joints looked OK. He didn't like risking a blow seal. If I get my wife's Tahoe out of the garage today I will check it this weekend.

 

Some of this stuff is just too hard for a "real" mechanic to do.

 

Bernie

[Mark Shaw 1,676]

3 hours ago, Terry Wiegand said:

tire and wheel balance.

This is the first thing to check....

[FLYER15015 777]

Rod,

You running bias ply or radials ?

From whom ?

Jack her up and give them a spin.

Do they "track" straight ? Or wobble side to side ?

 

I solved an intermittent shimmy with "balance beads" in the tires.

 

Mike in Colorado

 

[Bloo 1,663]

7 hours ago, auburnseeker said:

Wouldn't 35 lbs be overinflated, causing you to ride on the center of the tire and not the full tread path?

 

Most likely about perfect if they are steel belted radials. If they are original-type

crossply tires, yeah, probably too high.

 

7 hours ago, Rod Frazier said:

Perfect alignment has never been possible with this car, which will always pull slightly to the left

 

I agree with Trimacar that this needs another look. If it is caused by anything OTHER than thrust angle, it is almost certainly related to the trouble you are having. Even If it is thrust angle I would be looking into WHY.

 

 

Edited September 20, 2019 by Bloo (see edit history)

[Bloo 1,663]

25 minutes ago, FLYER15015 said:

Jack her up and give them a spin.

Do they "track" straight ? Or wobble side to side ?

 

This cannot be overstated. Look for up and down motion as well as side to side.

 

If you see up and down motion as well as a snakelike deformation in the tread, that is what a slipped belt in a radial tire looks like. Don't keep driving if you see that.

 

In some other thread recently there was a post where a tire (I believe it was a replica crossply) was mis-manufactured, and the tread wobbled from side to side as it ran. It was on a straight-axle car, and yes those are far more prone to wobble, tramp, etc than a 40 Buick, but when the good tire was upset by a bump and lost grip, the wobbly tire would set up a wobble that would persist until the car slowed way down or stopped. If you think about it, this could probably happen on just about any car.

 

[Rod Frazier 52]

Lots of good advice here, guys!  Tire pressure was low so I bumped it to 38 and it made a significant difference.  The shake is still there, but reduced to a level I can stand for another 400 miles until I get to Rock Hill for the tour.  I’ll be there for 5 days, which will give some time for a more serious look at the problem.  The alignment situation is puzzling and annoying but has never caused a shimmy in the past.  Most likely I have something else overly worn or out of adjustment.  Pretty drive through Kentucky today!

[auburnseeker 4,513]

Do the rims have a problem with 38 lbs?  Seems like alot of stress on the sidewalls of them. 

[Rod Frazier 52]

Never thought of that.  Something else to worry about?

[trimacar 3,234]

10 hours ago, Terry Wiegand said:

David, please explain to us on here why perfect alignment is not possible on these cars.  On my wife's LeSabre we had to replace one side of the tie rod ends.  The tire shop did an alignment using what I think was a laser based machine and the fellow told me that it was set to be dead on to factory specifications.  I would think that if this can be done on a car such as this, then it could be done on an automobile that has wheels that are not that much different from what is being used today.  Just asking.

 

Terry Wiegand

South Hutchinson, Kansas

Rod stated in his post that he's never been able to get perfect alignment with his car, it pulls to the left.  Indicates other problems with front end...

[Larry Schramm 3,126]

How old are the tires?  Has the car been sitting for a long time and possible flat spots on the tires?

 

On tire pressure, look on the side wall for the maximum tire pressure and you can safely run it at that pressure and get good tire wear and fuel economy.  The car will even steer easier. The car might ride a little harsher if you can even tell, but the benefits of the higher pressure out weigh the one negative.  I always run all of the tires on my vehicles at that pressure.

Edited September 21, 2019 by Larry Schramm (see edit history)

[auburnseeker 4,513]

If you run them at really high inflation as well, won't it crown the tire so you have less tire contact with the road.  An engineering friend always mentions this.  Run it through some soft dirt or just a little sand and see the contact of the tire.  He worries about alot of things , other guys don't consider.  I know on a rough road or those expansion cracks on the interstate will cause a light car like a Corvair to launch if the tires are overinflated. It happened to a friend until he dropped the tire pressure to the manufacture's recommendation.   Just passing on information that seemed to make sense to me.  

[Tinindian 1,699]

On 9/20/2019 at 4:45 AM, Rod Frazier said:

 Perfect alignment has never been possible with this car, which will always pull slightly to the left, but there’s no abnormal tire wear during the last 20000 miles.

I would wonder why???

I have been involved with auto mechanics for over sixty years, fourteen of them in dealerships and the last fourty-five in charge of company fleets.  I have never seen or heard of it being impossible to get a perfect alignment except for once. My car would pull sharply when going from pavement to gravel to dirt or over an angled railroad crossing.  I was told, by the dealership where I worked, that there was no point in aligning my '53 Buick Special as it was only out a small amount and it might be further out after an alignment.  Another dealership, Buick this time had the same answer.  On an old mechanics advice I took it to another Buick dealership.  They aligned it and it drove perfectly, 80 mph with no hands on a straight and level road and no problem going from pavement to gravel to dirt or crossing diagonal railroad tracks.

[trimacar 3,234]

Let me be clear, yes, you can get alignment that is as close to perfect as possible, but you CAN"T get that with WORN OUT FRONT ENDS.....there'll always be enough play in the many parts that make the alignment useless.

 

I'm guilty of it too, my '31 Pierce was restored in 1960, and driven around 60,000 miles on tours by previous owner.  He had no trailer, and drove the car to a lot of meets and tours in Louisiana and Texas from 1960 to the early 1980's.

 

When I was able to acquire the car, I, too, said, well, it's good enough, so let's keep driving it.  Engine fire in the 1990's, I restored the car with new paint, new upholstery, went through engine, and said to myself well, front end is "good enough".

 

Now, if I have underinflated tires, I get the death wobble.  I have a certain position on a hard left turn where the steering softly locks up, you have to put some force to it to make it get back where it should be.

 

A LOT of people, including me, say "good enough" on a restoration, when that's just kidding oneself.  You can align all you want, but if front end has other problems, it'll never be "perfect".

 

My best buddy puts it the best, it's like a car loan.  You can make a modest payment and pay it off, or you can skimp on payments and have a balloon note at the end.  Same with maintenance on an old car, you're going to pay to get it fixed either way..

[Rod Frazier 52]

On the alignment issue:  It is very close to spec and the pull is very slight, so I have put off dealing with it.  I’ve forgotten exactly what was out of whack, but one shop offered to fix it by heating and bending things to allow for more adjustment.  That didn’t seem like a good idea to me, and I am far from a good frame shop.  My Coker tires have 20,000 miles on them and are wearing normally ( but faster than I would like).

[Larry Schramm 3,126]

11 hours ago, auburnseeker said:

If you run them at really high inflation as well, won't it crown the tire so you have less tire contact with the road.  An engineering friend always mentions this.  Run it through some soft dirt or just a little sand and see the contact of the tire.  He worries about alot of things , other guys don't consider.  I know on a rough road or those expansion cracks on the interstate will cause a light car like a Corvair to launch if the tires are overinflated. It happened to a friend until he dropped the tire pressure to the manufacture's recommendation.   Just passing on information that seemed to make sense to me.  

 

Only if you run the tires at a pressure that is higher than the maximum pressure on the sidewall.  That tire pressure on the sidewall also tells you what the maximum load capacity of the tire.  When you run the tires at a pressure lower than the stated maximum pressure on that tire, the load range decreases.  Think of the Ford Explorer tire issue a number of years ago.  I am quite confident that between the lower tire pressure stated on the vehicle door and the loading of the vehicle, that is what contributed to a lot of the failures.  If the all of tires were inflated to the maximum pressure it would not have been such an issue.

 

One thing to thank for that whole story is the mandatory tire pressure monitor on all vehicles that started about 2005. I do not remember the exact date the regulation became required, but around that time. Maybe a little earlier.

 

Much of the manufacturers recommendations also take into consideration ride quality.  They are looking for a ride that is equal to the expectation of the customer for that particular vehicle.  Think about the different ride quality between a Cadillac and a 3/4 ton truck.  The truck tire pressures are probably around 70 psi because of the loads that the truck would be carrying and the Cadillac in the 40 psi range.  Higher pressure generally = higher load capacity for the tires and less heat generated.

 

That is also why trailer tires are usually at least 50 - 60 PSI.

[Barney Eaton 1,397]

All vehicles have specs for the alignment......even  new vehicles have a TOE spec.... I have seen both toe -in and toe -out spec.......why do you need that on a brand new vehicle with all new parts...TOLERANCE in the parts

Every connection has some movement,  when you add all the ball joints, tie rod ends, steering shafts, king pins...etc there will always be some slop caused by the tolerance build up.

To offset this condition the alignment spec calls for some TOE.    Setting the front with a little toe-in or out shifts those tolerances in one direction.   TOE setting is a compermises....no TOE and either front wheel can move right or left

using the tolerance in all the parts.   Too much TOE wears the tires.
I have never tried to measure new parts but suspect new tie rod ends may have .010 movement..... it only takes 6 connections to add up to .060 which is just under 1/16 of an inch.  

Now think about parts that have 10K or 40K miles and have additional wear and movement.   That 1/16 movement at the tie rod connection may turn into 1/4 inch movement at the tire tread.

We all know how old design tires want to move around on the road.........with slop/wear in the front suspension, one tire may want to go a little right,  then a little left.   The faster you are driving this right - left movement becomes shimmy.

that same tire is probably doing that movement at slow speeds but you do not see or feel the feedback in the steering wheel.

[valk 209]

Say that's a pretty car. Some serious driving lights there and I like the color scheme...

[neil morse 1,566]

Did you post here by mistake, Peter?  (Yes, your car looks great.)

[valk 209]

Naw, just liked the color combo as it's the same as mine (or close). And, yea, just showing off...never had a car this good. I'll pipe down...(no one likes a show off)

[neil morse 1,566]

😉😁

[Rod Frazier 52]

Found some worn bushings in the stabilizer links and new links are ordered and on the way to the hotel.  Just in case, am having the tires rotated and rebalanced tomorrow morning.  Fingers crossed!

[Rod Frazier 52]

Balance and rotation had no effect.  Thinking now that the shimmy is felt mainly through the seat rather than the steering, but still planning to install the new stabilizer links when they arrive.

[Mark Shaw 1,676]

6 hours ago, Rod Frazier said:

shimmy is felt mainly through the seat

Check the driveline balance...

[Rod Frazier 52]

Mark Shaw, I fear you may be right.  Butch at Vintage Cars did a detailed inspection for me last night and found no problem in the wheels, tires, suspension or steering.  Oh, for an open driveline!  Guess I’m just going to have to tolerate the shake until I get home to Utah.  2200 miles to go and I’m loving the drive anyway!

[1967 - 1997 Riviera 38]

Since you stated that the vibration is an "...intermittent shimmy...at all speeds, usually lasting 10 to 30 seconds before smoothing out again", and you've performed an inspection of tires, suspension and steering without pinpointing the problem, you might have what is known as a natural frequency or "beat frequency" vibration that is emanating from the drive line.

[Rod Frazier 52]

On the way home.  3000 miles under my belt, 1750 more to go.  Can’t wait to take things apart and get to the bottom of this problem.  The Glidden Tour (with a dozen beautiful Buick’s) was great fun, and I continue to be amazed at the beautiful scenery, especially in the mountains!  By the way, the car that was driven the farthest to get to the tour was a Buick!

[Marty Roth 2,551]

Rod,

 

Congratulations on yoour "LONG DISTANCE DRIVEN" trophy. I enjoyed talking with you at our table in the tent for the lunch, and sorry I didn't get to see you at the closing banquet, but wish you a safe trip home from the AACA GLIDDEN - and hope to visit with you again next year in Saratoga Springs, NY.

 

Maybe I'll have my '37 Roadmaster there next time.

 

Your car looked great on tour! 

[Rod Frazier 52]

Thanks, Marty, and sorry I didn’t get to the music night in time to join in.  Then again, THREE banjos could have been a tad excessive!🤪

[Rod Frazier 52]

Got home yesterday....5,062 miles without another problem except the driver's side wiper mechanism broke in Oklahoma!  Dreading that job.  I'm going to try swapping some tires/wheels with mine if I can find some  that will fit and, if that doesn't help the vibration - which I suspect it will not - then to try and figure out how to look for an imbalance in the driveline.  Keep the good advice coming, guys!

[Rod Frazier 52]

Success!  It was tires, after all.  Two hours of intensive road force balancing, including swapping tires and rims to find the best matches, solved the problem.  I drove her home 65 miles with nary a shimmy!  Thanks to all for the ideas and advice.